Driver

Note: this document discuss Mach-O port of LLD. For ELF and COFF, see LLD - The LLVM Linker.

Introduction

This document describes the lld driver. The purpose of this document is to describe both the motivation and design goals for the driver, as well as details of the internal implementation.

Overview

The lld driver is designed to support a number of different command line interfaces. The main interfaces we plan to support are binutils’ ld, Apple’s ld, and Microsoft’s link.exe.

Flavors

Each of these different interfaces is referred to as a flavor. There is also an extra flavor “core” which is used to exercise the core functionality of the linker it the test suite.

• gnu
• darwin
• link
• core

Selecting a Flavor

There are two different ways to tell lld which flavor to be. They are checked in order, so the second overrides the first. The first is to symlink lld as lld-{flavor} or just {flavor}. You can also specify it as the first command line argument using -flavor:

$ lld -flavor gnu

There is a shortcut for -flavor core as -core.

Adding an Option to an existing Flavor

1. Add the option to the desired lib/Driver/flavorOptions.td.
2. Add to lld::FlavorLinkingContext a getter and setter method for the option.
3. Modify lld::FlavorDriver::parse() in :file: lib/Driver/{Flavor}Driver.cpp to call the targetInfo setter for corresponding to the option.
4. Modify {Flavor}Reader and {Flavor}Writer to use the new targtInfo option.

Adding a Flavor

1. Add an entry for the flavor in include/lld/Driver/Driver.h to lld::UniversalDriver::Flavor.
2. Add an entry in lib/Driver/UniversalDriver.cpp to lld::Driver::strToFlavor() and lld::UniversalDriver::link(). This allows the flavor to be selected via symlink and -flavor.
3. Add a tablegen file called lib/Driver/flavorOptions.td that describes the options. If the options are a superset of another driver, that driver’s td file can simply be included. The flavorOptions.td file must also be added to lib/Driver/CMakeLists.txt.
4. Add a {flavor}Driver as a subclass of lld::Driver in lib/Driver/flavorDriver.cpp.